The present invention relates to the field of glass spacers, such as those applied in the area of prefabricated insulative multiple glazed windows and the like.
A critical requirement in modern building construction is energy conservation. A particular problem in view of the extensive use of glass in modern architecture is a loss of heat from the building through glass surfaces. One solution has been the increased use of insulating glass units, normally comprising at least two glass panes separated by a sealed dry air space. Sealed insulating glass units usually require some means precisely separating the two glass panels.
This leads to the conduction of heat from the interior glass plate to the exterior glass plate from where it is dissipated into the exterior environment. Further, there can result a differential dimensional change between the glass and the spacer, causing stress to develop on the glass and/or the seal which can result in damage to and the failure of the sealed glass unit.
There are several problems to be overcome in producing insulative multiple glazed windows wherein the panes are separated to form an insulative air space.
To provide the best insulative characteristics, the pane edges must be completely sealed to prevent communication between the air trapped between the glass panes, and the air in the environments on either side of the window (and/or in neighboring trapped air spaces in the case of windows having more than two glass panes). This has been traditionally done using a sealant material, such as a curable sealant adhesive, along the outside edges of the glass panes.
In order to best be able to produce a prefabricated multi-glazed window, it is necessary that the spacer be of substantially uniform thickness to maintain neighboring glass panes at correspondingly uniform distance from one another. This assures consistent sizing so that the balance of the window assembly can be predictably attached for installation.
Although the window spacer must restrict air flow, it must also prevent moisture from entering the trapped air space. If allowed in, moisture can condense inside the trapped air space, adversely affecting the translucence and appearance of the window. One common method of mitigating the effects of moisture has been to provide the spacer member with a desiccant material, such as silica gel, usually by placing the desiccant within a hollow spacer member, and providing small holes in the inside face of the spacer member to allow the desiccant to communicate with the trapped air space. While such an arrangement can reduce the effect of moisture in the trapped air space, the desiccants and the required machining of the spacer increase the cost of producing the window. Also, the amount of such desiccants in each window is limited by space constraints, and the desiccant cannot be regenerated in situ. Accordingly, desiccants have a limited capacity, and generally are normally exhausted after a few years of normal use, depending upon the ambient conditions.
One of the most serious and challenging problems in the production of window spacers is lack of insulative character in the spacer member itself. Typical spacers comprise hollow metal channels. Although they exclude moisture well, metals have high heat conductivity giving rise to the problem of low insulative character described above. In recent years, the insulative quality of window glass has increased to such an extent that the spacer member increasingly represents the weakest (i.e. most heat transmissive) portion of a multi-glazed window. The industry now recognizes that the spacer now accounts for a substantial portion of the total heat loss through an assembled multi-glazed window.
Metal spacers generally have expansion coefficients which differ from the glass and the sealant material. Also, because the metal/glass interface is difficult to seal, moisture can enter the trapped air space through this avenue.
There have been some attempts to use spacers made of polyvinylchloride rather than metal. This has, however been unsuccessful because the sealants which have been developed to construct reliable units bond well to glass and metal spacers, but not to polyvinylchloride spacers. This leads to structural weaknesses in units constructed with PVC spacers. Furthermore, the differential dimensional change that occurs between glass and PVC spacers over a certain range of temperature is much higher than with a metal spacer. In addition, most plastics have been found unacceptable for use between glass panes because they give off volatile materials, e.g. plasticizers, which can cloud or fog the interior glass surface.
The prior art shows some examples of the use of plastic over core material, but the details of construction and environment differ from the present invention. For example, U.S. Pat. No. 3,694,965 shows a wooden mullion element covered with a plastic extrusion, but this is not a spacer for double insulated glass. U.S. Pat. No. 3,070,854 shows a plastic channel member provided to cover a wooden separator between a pair of glass panes and U.S. Pat. No. 2,239,517 shows a metal separator provided with a plastic coating used in window construction.
U.S. Pat. No. 3,918,231 shows an extruded plastic element for fitting over a metallic frame element. U.S. Pat. No. 3,261,139 discloses a multiple glazed unit having a pair of resilient tape elements keyed to groves in the separator. U.S. Pat. No. 3,012,642 relates to window structures using very complex pane-holding elements. Canadian Patent No. 953,159 shows a double plated panel with a tubular spacer held in place by a non-hardening flow adhesive. German Offenlegungsschrift No. 1 434 283 also shows a spacer for double insulated glass.
U.S. Pat. No. 4,222,213 discloses an insulating spacer comprising an extruded or rolled-formed spacer together with a metal spacer together with a plastic insulating element which thermally insulates the metal spacer from the panes of glass while permitting conventional application of a sealant to provide reliable bonding. In one embodiment, the plastic insulator comprises an extruded plastic overlay which fits tightly over part of a conventional metal spacer. This patent discloses the incorporation of a metal spacer having portions for contacting in the sealant to provide a solid bond between the glass plate and the metal spacer. The spacer also incorporates a plastic insulator element to prevent any direct glass-to-metal spacer contact allowing only minimum contact with the glass plate to reduce heat conduction between the plates, while functioning as a spacer to keep the two glass plates at a measured distance during construction of a sealed window unit. However, the spacer taught by this patent is held mechanically affixed by contact pressure and/or friction. This patent teaches that this friction should not be so great that longitudinal shrinkage and expansion cannot occur with change in temperature due to different coefficients of expansion of the metal and plastic. This patent also teaches that some type of adhesive, such as EVA adhesive, could be used to insure permanent contact between the polymer and metal elements. However, this alternative is not preferred since it introduces the possibility of glass fogging, even when only small quantities of adhesive are used.
The '233 patent also teaches that many common extrudable plastics, such as PVC are not suitable for application in the disclosed spacer because they cause fogging of the glass.
Most recently, U.S. Pat. No. 5,088,258 disclosed an insulating spacer assembly comprising an extruded or rolled-formed hollow metal spacer together with thermal breaks and primary sealant. The spacer and thermal brakes may be coextruded together. However, this patent fails to teach the formation of a metal-polymer composite through the use of a heat-activated adhesive, as is done in the present invention.
U.S. Pat. Nos. 4,222,213 and 5,088,258 are hereby incorporated herein by reference.
The present invention represents an improvement over the prior art in that it allows for the use of a metal-polymer composite as a glass spacer while eliminating both concerns over differential expansion between the metal component and the polymer component, and the potential for fogging of the glass brought about by volatiles where adhesives are used.
The present invention also eliminates a concern over the use of extrudable polymers which normally would be unsuitable because they can give off volatiles, such as plasticizers.
The present invention therefore provides a glass spacer having precise and predictable dimensional characteristics, and excellent thermal insulative qualities. The present invention also eliminates concerns over fogging caused by volatiles in the polymer or the adhesive used to bond the polymer to the metal spacer substrate. The glass spacer of the present invention also provides an excellent barrier against air and moisture to prevent fogging or accelerated degradation of the spacer seal.